The present invention relates generally to vehicle suspension systems, and more particularly to such a system advantageously used in track driven vehicles such as snowmobiles.
In accordance with a preferred form of the invention hereinafter illustrated and described in detail, the suspension system includes a generally rectangular rigid frame having a pair of spaced parallel beams fixed by transverse braces and extending longitudinally of the vehicle, each beam terminating downwardly in a skid or runner slidably contacting and supported by the inner surface of the vehicle track. Attached to the frame are front and rear assemblies for resiliently supporting the vehicle body by front and rear transverse rods mounted on the body. The front support assembly includes a pair of laterally spaced arms pivotally attached at their rear ends to a transverse brace carried by the frame and resiliently biased upwardly relative to the frame, their forward ends being attached to the body, desirably through a transverse rod pivotally attached to the body. Means are provided for adjusting the biasing force urging the forward ends upwardly so that the user can select the desired ride and related handling characteristics of the vehicle.
The rear support assembly of the system includes a transverse rod carried by the body and resilient means in the form of a centrally disposed compression spring carried by the frame for resiliently biasing the rod upwardly relative to the frame through a linkage providing progressive springing action whereby to afford a soft cushiony ride over minor ground irregularities, while providing stiffer springing when the vehicle passes over large bumps or hummocks at increased speed. The rear support assembly also desirably includes a shock absorber acting in conjunction with the compression spring as well as means adjustable by the user for selecting the normal compression imposed on the spring, so that users having body weights within a wide range -- say 65 to 115 kg -- can, by proper setting of the adjustable means, enjoy substantially the same riding comfort on the vehicle. The linkage translating vertical frame movement into compression of the spring includes pivotal components whose pivotal axes form a triangle which flattens as the body is displaced downwardly, and the change of altitude of the triangle is vectorially added to the component of frame movement compressing the spring. The rate of altitude change increases rapidly as the parts approach maximum excursion, thus providing the progressively stiffening spring action.
It is accordingly a principal object of the invention to provide a novel suspension system for a track driven vehicle such as a snowmobile. Other objects and purposes are to provide, in such a system, front and rear support assemblies each including selectively adjustable means by which the user can choose desired riding and handling characteristics of the vehicle; to provide a rear support assembly including a resilient member and novel linkage means for translating movement of the resilient member into progressive springing action for enabling the rear assembly to provide safe and comfortable riding qualities over a wide range of severity of vertical track displacement resulting from ground irregularities; to provide such a system which is compact in size and light in weight, and accordingly well suited for a one- or two-occupant vehicle; and for additional objects and purposes as will be understood from the following description of a preferred embodiment of the invention, taken in conjunction with the attached drawings.